Add slider parameters as text decorations in flex plots

[Gregory Smith]

It would be useful if you are generating plots for publication to have the slider values documented. I was wondering if you thought it was worthwhile to add them as small font text decorations in a corner of the plot area (or outside the plot area).

This would be applicable for flex plots, flex trend, box plot, and force curve plots.

[Sander Roosendaal]

Issue #451 was marked as a duplicate of this issue.

[Sander Roosendaal]

Flex chart, cumulative flex charts done

[Sander Roosendaal]

trend flex done

[Sander Roosendaal]

box plot done